KLK3 and germ cell tumor: For example, several investigators have observed that the abnormal expression of different glycosylated proteins were implicated in disease and that changes in the level of glycoprotein could be used as hallmarks for disease diagnosis, including the carbohydrate antigen CA-19-9 for colon cancer [8], the prostate-specific antigen (PSA) for prostate cancer [9], α-fetoprotein for liver cancer [10], and β-human chorionic gonadotropin for germ cell tumors [11].